JP 2005-32712 A, for example, discloses a lithium-ion secondary battery. The publication discloses that the lithium-ion secondary battery is filled with an electrolyte solution in which LiPF6 serving as an electrolyte is dissolved in a mixed organic solvent of 3:7 volume ratio of ethylene carbonate and diethyl carbonate and LiPF2(C2O4)2 is further added thereto. It also discloses that the addition of an appropriate amount of LiPF2(C2O4)2 significantly improves the output power performance at low temperature. It describes that the reason for the significant improvement in the output power performance at low temperature is that at least a part of the additive agent LiPF2(C2O4)2 is decomposed during initial charging to form a stable surface film on the surfaces of the positive electrode and/or the negative electrode as well as the surfaces of the positive electrode active material and/or the negative electrode active material. It is considered that the surface film activates the interface between the active materials and the electrolyte solution (i.e., the interface between the electrodes and the electrolyte solution), allowing smooth insertion and deinsertion of lithium ions.
JP 1994-302337 A discloses a non-aqueous electrolyte battery in which at least one kind of solvent that constitutes an electrolyte solution is impregnated into at least one of positive and negative electrodes and thereafter separators are interposed between the positive and negative electrodes to produce a battery element. The publication also discloses that, in another embodiment, a non-aqueous electrolyte battery is produced by impregnating at least one kind of solvent that constitutes an electrolyte solution into a battery element having positive and negative electrodes and separators interposed between the positive and negative electrodes, thereafter enclosing the battery element into a battery case, and then filling the electrolyte solution containing the remaining constituent components into the battery case. According to the publication, this allows the electrolyte solution to be impregnated into the battery element smoothly.